Saying that a 64 GB SD card makes no sense in a Z1C, might be true for you, but there are plenty of scenarios to fill up a SD card.
Some apps and games have the option to store additional data on the SD card.
For instance NavFree can store maps on the SD card.
When you store 720p (or even 1080p) high bit rate movies on your SD card, it can fill up quite quickly (Gigabytes per movie).
Photos and movies made with the camera can be stored on the SD card.
A lot of people I know have large music collections stored on SD cards in their phones.
